RCON™

CONCRETE ELECTRICAL RESISTIVITY METER

OVERVIEW

Giatec RCON™ is an advanced tool for the electrical resistivity measurement of concrete using uniaxial method.

RCON™ employs AC impedance technique for the accurate and fast readings that can be continuously obtained

using its customizable and user-friendly operating software for various concrete materials. The electrical

resistivity of concrete can be simply related to their pore network characteristics such as pore size and their

connectivity, moisture content in the pores and pore solution chemistry. In concrete materials, the electrical

resistivity has been correlated well with important durability parameters such as permeability and diffusivity.

In addition, this non-destructive test can be easily conducted on fresh or hardened concrete specimens at

different ages or various stages of hydration in order to study workability, setting and durability performance of

concrete. The electrical resistivity method has also been applied to investigate corrosion of rebar in concrete,

creep, aggregate segregation and freeze and thaw of concrete since they affect the pore network properties.

FEATURES

Fast (<5 Second)

Accurate (±2%)

AC measurement (Galvanostatic)

Wide range of measurement frequencies (1Hz to 30kHz)

Phase detection (0-180 degree)

Stand alone operation

Continuous measurement

User-friendly PC software

Flexible sample holders

Customizable setup

USB connection to computer

MEASUREMENT CONCEPT

Giatec RCON™ applies a small alternating current at intended frequencies without causing any disruption and

measures the voltage between the two ends of the concrete specimen. The impedance (Z ) can then be

calculated from measured voltage and applied current values. In order to apply the current, two conductive plates

are used as shown in Fig. 1. Concrete resistivity is then determined using the impedance value as follows:

Eq. 1

where .cm] is the resistivity, A [cm2] is the cross-sectional area of the specimen, L [cm] is the length of the

specimen, and Z is the impedance (resistance) measured by the device.

Figure 1: Concrete specimen placed between two plates

The current signal generated by the device is sinusoidal. The voltage measured across the specimen is divided by

the imposed current to obtain the impedance (See Fig. 2-a). Based on the value of the impedance, the current

scale may vary from 10µA to 1 mA.

The phase of the impedance is calculated by determining the difference between the phase of the voltage and

current (See Fig. 2-b).

APPLICATION

RCON™ is a unique tool to investigate the micro-structural properties of concrete including:

A) PERFORMANCE-BASED QUALITY CONTROL OF CONCRETE

Concrete electrical resistivity techniques is a suitable replacement for the Rapid Chloride Permeability Test of

concrete (as per ASTM C1202 or AASHTO 277) since there is a good correlation between the bulk electrical

resistivity and durability performance of concrete (See Table 1). Therefore, this technique can be used for the

performance-based quality control of concrete.

Table 1: Rapid chloride permeability and bulk electrical resistivity values1

Chloride Penetration 56-Day Rapid Chloride

Permeability Charge Passed as per ASTM C1202 (Coulombs)

28-Day Bulk Electrical Resistivity of Saturated

Concrete (kΩ.cm)

High >4,000 <5

Moderate 2,000-4,000 5-10

Low 1,000-2,000 10-20

Very Low 100-1,000 20-200

Negligible <100 >200

a) Impedance measurement concept b) Measurement blocks

Figure 2: Impedance measurement concept

B) DIFFUSION OF CHLORIDE IN CONCRETE

An almost linear correlation between chloride diffusion coefficient determined through ponding test and

conductivity (1/, where was measured using uniaxial technique with AC current at 1 kHz frequency) was

reported by Ghods et al. (see Fig. 3)2. Similar findings have been reported by Sengul and Gjørv3.

C) CORROSION OF REBAR IN CONCRETE

Investigations have found correlations between concrete resistivity and both, the corrosion initiation and the

propagation period. The corrosion rate often has an inverse correlation to the electrical resistivity. Hornbostel et

al.4 have gathered a comprehensive literature review on the relation of corrosion rate and electrical resistivity and

the contributing factors. In general, higher electrical resistivity of concrete lowers the risk and the rate of

corrosion (Table 2).

Table 2: Relation between concrete resistivity and severity of corrosion5

Resistivity (k.cm) Severity of corrosion

>20 Low corrosion rate

10-20 Low to moderate corrosion rate

5-10 High corrosion rate

<5 Very high corrosion rate

Figure 3- Relation between electrical conductivity and chloride diffusion coefficient of

concrete for twenty mixture propotions2

R² = 0.93

0

5

10

15

20

0.00 0.01 0.01 0.02 0.02

Diffu

sio

n C

oeff

icie

nt

(m2/s

ₓ 1

0-1

2)

Conductivity, 1/, S (ῼ.m)-1

D) SETTING TIME OF FRESH CONCRETE

The concept of electrical resistivity has been used to develop test methods for determining the setting time of

cement, mortars and concrete. Li et al.6 have investigated the hydration process and setting times of fresh

concrete using electrical resistivity (Figure 4). Gu et al.7 also investigated the microstructural characteristics of

hydrating cement-silica fume system using A.C. impedance spectroscopy.

Figure 4- Comparison between setting times of fresh concrete using ASTM C403 and electrical resistivity method6

E) MOISTURE TRANSFER IN CONCRETE

One potential application of electrical resistivity method is to determine the moisture content of concrete.

Several research have shown that the electrical resistivity is significantly affected by moisture content8,9; however,

the application and reliability of the method to determine the moisture content is yet to be studied. Shekarchi et

al. used electrical resistivity technique to monitor the water content of concrete in large elements (Figure 5)8.

Figure 5- Comparison between water content of hardened concrete obtained directly by drying technique and

indirectly by electrical resistivity technique8

0

5

10

15

20

0 2 4 6 8 10 12 14 16 18

Settin

g T

ime b

y R

esis

tivity

(hours

)

Setting Time by Penertration Test (hours)

ti

tf

ti= initial setting time, tf= final setting time

F) MICRO-CRACK DEVELOPMENT IN CONCRETE

The electrical resistivity technique can also be used to detect cracks in concrete. However, it is noted that several

parameters could affect the readings in this case. Salehi10 carried out a numerical study on the effect of cracks and

presence of steel rebar on electrical resistivity of concrete. Wiwattanachang11 also investigated the development

of cracks in fiber concrete beams using electrical resistivity technique. Recently the relationship between electrical

resistivity change and micro-cracks development in reinforced and unreinforced concrete was studied by a

number of researchers12,13 (Figure 6).

Figure 6- The change in electrical resistivity with the development of micro-cracks in concrete under tensile

load13

Micro-crack development zone

TECHNICAL SPECIFICATIONS

Reading Range and Accuracy

Reading Range Frequency spectrum

Phase measurement

Impedance accuracy

Phase accuracy

1 -100 Ω

1Hz - 30KHz 0-180°

±2% ±2digit

5% ±3digit

0.1-1K Ω

1 -10K Ω

10 - 100K Ω

0.1 - 1MΩ 1Hz - 10KHz

Measurement Time

Frequency Sampling time Reading time (minimum)

1Hz - 4Hz 5 seconds 10 seconds

5Hz - 30KHz 1 second 2 seconds

Operating Conditions

Type Value

Operating temperature 15C - 45C

Operating humidity 30% - 80%

Storage temperature 0C - 60C

Storage humidity 5% - 90%

Operating voltage/current 100 - 240 V, 50/60 Hz

Dimensions 200 x 230 x 70 mm

Data acquisitions software (PC software) Yes

Note: Specifications are subject to change without notice.

REFERENCES

1. Shane, J.D., Aldea, C.M., Bouxsein, N.F., Mason, T.O., Jenning ,H.M., Shaw, S.P. (1999),” Microstructural and

pore solution changes induced by rapid chloride permeability test measured by impedance spectroscopy”,

Concrete Science and Engineering, Vol. 1, pp. 110-119.

2. Ghods, P; Chini, M.; Hoseini, M., Alizadeh R. (2005), “Evaluating the chloride diffusion of concrete by

measuring electrical resistivity”, Intl. Cong. on Global Construction: Ultimate Concrete Opportunities, Proc. of

the Intl Conf. on Young Researchers' Forum, Dundee, Scotland.

3. Sengul, O., Gjørv, O. E. (2008), “Electrical Resistivity Measurements for Quality Control during Concrete

Construction”. ACI Materials Journal, Vol. 105(6), pp. 541-547.

4. Hornbostel, K; Larsen, C. K., Geiker, M. R. (2013), “Relationship between concrete resistivity and corrosion

rate – A literature review”, J of Cement and Concrete Composites, Vol. 13, pp. 60-72.

5. ACI Committee 222R-01 (Reapproved 2010), “Protection of metals in concrete against corrosion”, American

Concrete Institute, Farmington Hills, Michigan.

6. Li, Z., Xiao, L., and Wei, X. (2007), “Determination of Concrete Setting Time Using Electrical Resistivity

Measurement”, Journal of Materials in Civil Engineering, Vol. 19, pp. 423-427.

7. Gu P., Xie, P., Beaudoin, J. J., and Brousseau, R. (1993), “A.C. Impedance Spectroscopy (II): Microstructural

Characterization of Hydrating Cement-Silica Fume Systems”. Cement and Concrete Research, Vol. 23(1), pp.

157–168.

8. Shekarchi, M., Debicki, G., Billard, Y., Briot, R. (2001), “Nondestructive Monitoring Technique Based on

Electrical Resistivity for Moisture Condition in Containment Structures”, SMiRT 16, Washington, DC USA, pp.

1409-1414.

9. Brameshuber, W., Raupach, M., (2003), “Non-destructive Determination of the Water-Content in the

Concrete Cover using the Multi-ring-Electrode, PART I: ASPECTS OF CONCRETE TECHNOLOGY”, BB

85-CD International Symposium, Non-Destructive Testing in Civil Engineering (NDT-CE), Berlin, September

16-19.

10. Salehi, M. (2013) “Numerical investigation of the effects of cracking and embedded reinforcement on surface

concrete resistivity measurements using Wenner Probe”, M.Sc. Thesis, Carleton University.

11. Wiwattanachang, N., Giao, P. H., (2011), “Monitoring crack development in fiber concrete beam by using

electrical resistivity imaging”, Journal of Applied Geophysics, Vol. 75, pp. 294-304.

12. Pacheco, J., Šavija, B., Schlangen, E., Polder, R. B., (2012), “Relationship Between Cracking And Electrical

Resistance In Reinforced And Unreinforced Concrete”, 2nd Intl. Conf. on Microstructural-related Durability of

Cementitious Composites, Amsterdam, Netherlands.

13. Lin, V. W. J., Li, M., Lynch, J. P., Li, V. C., (2011), “Mechanical and electrical characterization of self-sensing

carbon black ECC”, Proc. SPIE 7983, Nondestructive Characterization for Composite Materials, Aerospace

Engineering, Civil Infrastructure, and Homeland Security 2011, 798316 (April 18, 2011)

© Giatec Scientific Inc.

301 Moodie Dr., Suite 302 Ottawa, Ontario, K2H 9R4 Canada

Tel: +1 (613) 858-1895 Fax: +1 (613) 280-1544 http://www.giatec.ca V14-01